1. Field of the Invention
The present invention relates to an aqueous cosmetic or dermatological preparation which preferably comprises particles in a suspended state.
2. Discussion of Background Information
For aesthetic reasons in particular, transparent and translucent products are preferred by many consumers. Thus, transparent formulations are often used, for example, as deodorant or antiperspirant (AP). These can nowadays be realized by the following technologies:                1. aqueous-alcoholic formulations        2. water-in-silicone emulsions        3. microemulsions        
Aqueous-alcoholic deodorant and AP formulations are mostly based on water and alcohol as medium, deodorant and antiperspirant agents as active ingredients, and also perfume, solubilizers and thickeners (mostly based on carbohydrate) as additional agents. They are perceived by the consumer as being fresh and cooling, but are at the same time encumbered with a whole series of disadvantages. Thus, for example, application primarily to freshly shaved skin is associated with incompatibilities as a result of the alcohol content. Another major disadvantage is the fact that relatively large amounts of oil cannot be incorporated into such systems. As a result of the high content of antiperspirant salt required for highly effective performance, a white residue remains following application to the skin; this is perceived by the consumer as being extremely troublesome. However, due to the absence of a sufficiently large oil phase for technical reasons, this residue cannot be concealed. Moreover, the use of carbohydrate thickeners leads to high stickiness of the product after the alcohol has evaporated.
Water-in-silicone emulsions belong to the group of water-in-oil emulsions. The water phase comprising ethanol or polyhydric alcohols, such as, for example, propylene glycol and water-soluble active ingredients, such as AP agent and/or deodorant active ingredient, constitutes about 75-90% of the formulation. The oil phase consists of a volatile and a non-volatile silicone oil and also a silicone emulsifier.
The transparency of water-in-silicone emulsions is based on matching the refractive indices of the two phases. It is a drawback that even a difference in the indices of 0.0004 caused, for example, by evaporation, leads to cloudiness. WO 98/32418 and WO 92/05767, the entire disclosures whereof are expressly incorporated by reference herein, describe such deodorant or AP formulations based on W/S emulsions.
One approach for solving the described disadvantages has been made possible through cosmetically pleasing alcohol-free and transparent products which are based on so-called microemulsions. These have the major advantage that even relatively large amounts of various oils—with all of the described positive effects for the consumer—can be stably incorporated. Formulations of this type are in principle available by means of phase inversion temperature technology (PIT) or high-pressure homogenization. The required stability of the emulsifier system to high concentrations of antiperspirant salts, however, places high demands on the formulation skill of the product developer.
WO 98/15255, the entire disclosure whereof is expressly incorporated by reference herein, describes microemulsions. However, a drawback even with these formulations is a sticky feel on the skin caused by the thickener, and the lack of a yield point.
In view of the foregoing, it would be advantageous to have available a cosmetic or dermatological preparation which is transparent or translucent and preferably exhibits low, if any, stickiness. In particular, it would be desirable to provide a cosmetic or dermatological preparation which is transparent and has no cloudiness at all, is characterized by a minimized stickiness and has a defined yield point for optimized discharge and application.
In the field of antiperspirants it is customary to increase the amount of antiperspirant active ingredient, such as, for example, aluminum chlorohydrates (ACH) to increase the antiperspirant effectiveness. Furthermore, so-called activated aluminum chlorohydrates (AACH) are known as antiperspirant active ingredients with increased effectiveness, see, e.g., EP 925783 or Antiperspirants and Deodorants, 2nd Edition, Cosmetic and Technology Science, Vol. 20, 1999. The entire disclosures of these documents are expressly incorporated by reference herein.
However, by increasing the amount of active ingredient the antiperspirant effectiveness can be increased to only a limited degree because above a content of about 15% by weight of the AP active ingredient, saturation of the effectiveness is established and in addition disadvantages such as white residues and an unpleasant feel on the skin are increased.
If an aluminum salt AlX3 of a strong acid (e.g. AlCl3) is dissolved in water, then, in accordance with the equation:AlX3+6H2O→Al (H2O)63++3X−the octahedral hexaaquaaluminum ion [Al(H2O)6]3+ is formed, which acts as a weak cationic acid.
As a consequence of the acidic effect, the hexaaquaaluminum ion is liable to hydrolysis and can be successively deprotonated to form the hexahydroxoaluminate ion [Al(OH)6]3−.
Depending on the pH and the concentration of aluminum ions, three-dimensional structures are formed as a result of bridging with hydroxide ions and oxygen atoms. These processes, in which element atoms are bridged by hydroxide ions, are called olation and for bridges with oxide ions, the term used is oxolation.
Both reactions belong to the group of condensation reactions.
The polynuclear aluminum cations [Alm(OH)n(H2O)o]p+ which are present in aqueous aluminum salt solutions belong to the group of isopolyoxo cations.
In order to achieve an increased antiperspirant effectiveness of classic aluminum chlorohydrate (ACH) solutions, the solutions may be thermally treated by using suitable concentration, temperature and pressure ranges, and the resulting solutions may be dried by means of spray-drying. This leads to an increased amount of molecules of smaller size being present in stable form. However, in water these activated aluminum complex salts (AACH) which are effective as antiperspirants disintegrate back to their original equilibrium state, thereby losing their increased effectiveness.
Use of these activated ACH (AACH) types has therefore hitherto only made sense in nonaqueous systems since otherwise reconversion to the molecular size distribution as occurs in classic ACH solutions is likely to occur, as described, for example, in the article by A. H. Rosenberg—Antitranspirant Technology, SÖFW-Journal, 128 (4) 2000, the entire disclosure whereof is expressly incorporated by reference herein.
It would be desirable to provide an aqueous cosmetic or dermatological preparation without the described disadvantages. In particular, it would be advantageous to have available aqueous cosmetic or dermatological preparations which, despite their water content, comprise a significant concentration of activated aluminum complex salts.
Additives are often added to cosmetic or dermatological preparations such as, e.g., antiperspirant formulations in order to increase the convenience or optical acceptance.
However, it is often impossible to incorporate suitable visible particles in stabilized form such that the particles do not sink, particularly in the case of a relatively long standing time, and do not mix with the remaining constituents of the formulation.
It would therefore also be desirable to provide a cosmetic or dermatological preparation which makes it possible to incorporate particles in stably suspended form without the particles sinking, particularly in the case of a relatively long standing time, or the particles mixing with the remaining constituents of the preparation into which they are incorporated.